The present invention relates to airfeed tools, more particularly the present invention relates to air logic circuits for airfeed tools.
The use of peck drilling in heavy industry, particularly industry which requires the drilling of a plurality of holes in a variety of metal pieces, has shown a dramatic increase in recent years. This is because the holes resulting from a peck drilling operation exhibit greater accuracy then holes drilled by conventional drilling operations. Additionally, the surface finish of the hole is much smoother than obtained with conventional drills.
U.S. Pat. No. 4,123,188 to Deremo et al. and U.S. Pat. No. 4,421,441 to Hirose are representative of the design of airfeed peck drills. Such prior art airfeed peck drills include a motor and reduction gearing which is contained within a cylinder to form a drill quill which is attached to the end of an air cylinder. The air cylinder in these prior art drills is used to advance and retract the drill quill into an out of a workpiece. In order to prevent the drill quill from feeding forward before being fully retracted, the back pressure created by the returning quill is used as a signal.
On newer airfeed drills, different sized areas are used on the feed-retract piston. The air logic circuitry as taught in U.S. Pat. No. 4,123,188 will not provide the necessary signal to prevent the tool from feeding forward until fully retracted.
There is therefore a need in the art to provide an air logic circuit which will prevent airfeed peck drills having different sized areas on either side of a feed retract piston from feeding forward until fully retracted.